1. Field of the Invention
The present invention relates to a radiographic system that radiographs a tomographic image using radiation and a control method of the radiographic system.
2. Description of the Related Art
In the medical fields, radiographic systems using radiation such as X-rays are known. A radiographic system includes an X-ray generator including an X-ray source generating X-rays and an X-ray imaging apparatus receiving X-rays and capturing an X-ray image. As an X-ray imaging apparatus, an X-ray image detector using as a detection panel a flat panel detector (FPD) in which pixels accumulating signal charges corresponding to the dose of X-rays are arranged in a matrix shape has been widely spread. The FPD accumulates signal charges in the respective pixels and converts the accumulated signal charges into a voltage signal through the use of a signal processing circuit, whereby an X-ray image representing image information of the subject is detected and is output as digital image data.
A radiographic system is known which detects the dose of X-rays passing through a subject through the use of a dose sensor and performs an automatic exposure control (AEC) of stopping irradiation with X-rays from an X-ray generator when the integrated value of the doses reach a predetermined threshold. In a radiographic system including plural dose detectors, a detection field corresponding to a region (also referred to as “a region of interest (ROI)”) to which attention should be most paid is set for each radiographing site and the irradiation stop of X-rays is determined on the basis of the X-ray dose from the dose sensors in the detection field.
A radiographic system is also known which performs a tomosynthesis imaging of causing an X-ray source to move and irradiate a subject with X-rays from different irradiation angles to perform plural radiographing operations and reconstructing plural images acquired through the radiographing operations to generate a tomographic image in which a desired tomographic plane is emphasized. In the tomosynthesis imaging, the distance traversed by X-rays passing through a subject, that is, the thickness of the subject, varies depending on the irradiation angle of X-rays. Accordingly, when the tomosynthesis imaging is performed with a fixed dose, the density of the detection field of each image differs. Therefore, in radiographic systems described in JP2000-501552T and JP2008-253555A, the variation in thickness of a subject is predicted on the basis of the irradiation angle of X-rays and the subject is irradiated with X-rays of the dose corresponding to the predicted thickness of the subject.